Method and means of precooling insulated tanks for storing cold liquids



Aug. 30, 194. .s. o. .mcKsoN 5 METHOD AND MEANS OF PRECOOLING INSULATEDTANKS FOR STORING COLD LIQUIDS Filed Sept. 20, 1944 2 Sheets-$heet lFiled Sept. 20, 1944 8- 1 J. o. JACKSON 2,480,472

METHOD AND MEANS OF PRECOOLING INSULATED 2 Sheets-Sheet 2 TANKS FORSTORING COLD LIQUIDS J l A 1 Patented Aug. 30, 1949 S PATENT OFFICEMETHOD AND MEANS OF PRECOOLING 1N- SULATED TANKS FOR STORING COLDLIQUIDS James 0. Jackson, Grafton, Pa., asslgnor to Pittsburgh-DesMoines Company, a corporation of Pennsylvania Application September-'20,1944, Serial No. 554,924

9 Claims.

This invention relates to double walled insulated tanks used asreservoirs for storing above ground relatively great quantities ofliquefied gas, such as liquefied natural gas, liquefied oxygen,liquefied propane, etc.

Several forms of double walled insulated tanks adapted to serve asreservoirs for storing such liquefied gases are disclosed in anapplication filed by me January 9, 1942, numbered 426,192 and sinceabandoned.

A serious problem encountered in placing in service tanks such as these(when the inner shell of such tank is fabricated from a metal such asferrous metal) is that occasioned by thermal shocks and stresses due touneven cooling when such shell is charged with these extremely coldliquefied gases. This is liable to rupture or crack some portion of suchinner shell structure and thus render the entire tank useless.

The invention of this application relates particularly to a method andmeans for precooling the inner shell structure of such double walledinsulated tanks or containers in order to condition them to receive andstore liquefied gas without harmful thermal shock or stress.

This invention has as one of its objects the provision of an improvedmethod of cooling down all parts of the inner shell structure of suchdouble walled insulated tanks or containers from the prevailing ambienttemperature to approximately that of the low temperature liquid to bestored therein.

Another object is the provision of means for carrying out the method ofthis invention.

A further object is to produce a double walled insulated storage tank orreservoir for liquefied gas, which in its make-up includes means wherebyall interior parts of the inner shell structures thereof can be slowlyand substantially uniformly cooled from the prevailing ambienttemperature to approximately that ofthe liquefied gas to be storedtherein.

These and other objects, I attain by the method and apparatus describedin the specification and illustrated in the drawings accompanying andforming part of this application.

' In the drawings:

Figure 1 is a sectional view in elevation of a double walled insulatedtank for storing liquefied gas, equipped with means for conditioning orprecooling the inner shell structure of such tank in accordance with themethod of this invention.

Fig. 2 is an enlarged side sectional view of 2 the tank boot .with theparts enclosed thereby in elevation;

Fig. 3 is a view such as Fig. 2 but is taken at thereto looking down.

Figs. 4, 5, 6 and 7 are enlarged sectional views of coils comprised inthe means for carrying out the precooling method of this invention.

The method of this invention can be utilized for the conditioning orprecooling of any type of insulated tank or container designed to serveas a storage reservoir for low temperature liquids, such as liquefiednatural gas, liquefied methane and its homologs, liquefied ethane,propane and butane, as well as other liquefied gases such as liquidoxygen, liquid nitrogen, etc.

For the purposes of this application, I have illustrated my method inconnection with one form of storage tank or container disclosed in mysaid application 426,192. This, it is to be understood, is without anyintent of limiting this invention to any particular form or type ofstorage tank or container, since both my method and the apparatus forcarrying out such method can be used for conditioning or precooling anytype of insulated tank or container for storing low temperature liquids.It is of particular value, however, when those portions of the tank orcontainer, contacted by the stored liquid, are fabricated from metalthat is subject to damage from thermal shock or stress, and when thesizeof the tank or container is great enough to make slow substantiallyuniform precooling necessary or worth while.

The method of this invention broadly comprises conveying precoolingfiuidinto the interior of the inner shell of the tank or container, inso directing small jets of such fluid that substantially all interiorparts of such inner shell structure are contacted thereby, and inperiodically lowering the temperature of the precooling fluid in such anamount that the difference between the warmest part of the inner shellstructure and the temperature of such precooling fluid is never so greatthat such precooling fluid will cause harmful thermal shock or stress inany part of such inner shell structure.

A storage tank such as disclosed in my said application 426,192 andillustrated in Fig. 1 of the drawings of this application has been builtand is now in successful operation. Such tank was designed to store160,000 cubic feet of liquefied natural gas under a maximum Workingpressure of about 5 pounds per square inch gauge. This quantity ofliquefied gas upon evaporation produces million cubic feet of gas.

Such tank is of welded construction and comprises inner and outer spacedcylindrical shells. The inner shell is about 70 feet in diameter and 43feet high. This shell is fabricated of low carbon steel having a nickelcontent of about 3.50% and a Charpy impact value of about foot pounds at260 F. V

The plates forming the roof ll and the bottom I2 of the inner shell canbe said to be spherically dished; the bottom plates downwardly and theroof plates upwardly.

The'outer shell [3 has a diameter of about 76 feet and a height of about51 feet and is fabricated from ordinary tank (medium carbon) steel. Thisouter shell has a flattened cone roof and the plates forming its bottoml5 can also be said to be spherically dished downwardly. The bottom ofthe outer shell parallels the bottom of the inner shell.

The tank is mounted on a concrete foundation l6 so constructed andarranged as to space the tank above the ground and permit circulation ofair therebeneath,

A space of about three feet separates the inner and outer shells andthis space is filled with finely divided dry insulating material I1. Thecontainer is equipped with automatic pressure and relief valves andrupture disks (numbered l8 as a group) to provide for safe operation.

A pipe I9 is provided for filling th tank with liquefied gas anddischarging liquefied gas therefrom.

A circular row of equally spaced column-like members located whollywithin and extending from the bottom of the inner shell to the roofthereof assists in supporting the roof of such shell.

The inner shell and its contents are supported by two concentriccircular rows of spaced wooden posts. The outer circular row of posts 2|is positioned directly below the cylindrical wall of the inner shell,while each post 22 of the inner circular row is placed directly belowone of the roof supporting column-like members 20. These posts are somounted that they are free to tilt radially with relation to the innershell, as such shell expands and contracts due to temperature changes.

A vent pipe 23 extending upwardly through the inner shell bottom has itsopen upper end 24 located adjacent the roof of the inner shell. Ventpipe 23 and pipe l9 extend outwardly from the tank through a metal boot25 which connects with the outer shell of the tank as shown in Figures1, 2 and 3. These pipes parallel one another, are provided withexpansion joints 26 and are encased in a jacket of sheet-like insulatingmaterial 21. The boot outside of such jacket is filled with finelydivided insulating material 28. Pipes l 9 and 23 connect with aliquefaction plant which is diagrammatically illustrated at 29.

When the construction of this storage tank was completed, it was cooleddown with cold natural gas which was circulated through the inner shellthereof until such shell was believed to be cold enough to receive thecold liquefied natural gas to be stored.

At the end of such cooling down period, liquefied natural gas was veryslowly run into the inner tank shell through the pipe I 9 which servesboth as inlet and outlet for the liquefied gas. After the bottom of theinner shell reached so low a temperature that some of the liquefied gasremained or collected at the bottom of the inner shell as a liquid, theflow of liquefied gas into the tank was gradually increased. When theliquefied gas had reached a depth of about one foot, the bottom of theinner shell ruptured and the liquefied gas which had been run into thetank was lost.

The ruptured bottom was repaired and the tank was then equipped withmeans for carrying out the method of this invention in order to insurethat all parts of the inner shell structure cooled down slowly anduniformly to approximately the temperature of the liquefied gas to bestored, which is about 258 F.

The means for carrying out this method includes four coils 30-33inclusive of inch copper pipe which were installed within the innershell. Coil 30 extends circumferentially of the inner shell and issecured to the interior thereof just below its roof. Coil 3i issimilarly placed around the interior of the inner shell about midwaybetween its top and bottom. Coil 32 surrounds and is carried by thecircular row of column-like members 20 adjacent the roof of the innershell. C011 33 surrounds and is supported by said columnlike members 20about midway between the roof and the bottom of the inner shell. Figures4-7 inclusive are enlarged transverse sectional views of these coils andit will be seen from these views that coils 30 and 3| are secured to theinner face of the inner shell by bars 34 and U-shaped rods 35 and thatcoils 32 and 33 are secured to columnlike members 20 by U-shaped rods 35having their ends welded to certain of such column-like members.

Throughout the length of each coil, small holes (indicated by thenumeral 31) of the order of .04 of an inch in diameter, are drilled.These holes are drilled at about one foot intervals and on a number ofdifferent axes, the choice depending on the portion of the coil withinthe inner shell and the portion of the shell structure the jets ofpreccoling fluid issuing from such holes are designed to reach.

These holes are of such number and are so positioned as to cause thejets of precooling fluid issuing therefrom to contact all parts of theinner face of the inner shell and all parts of the shell structure suchas supporting column-like members 20. Figs. 4 to '7 inclusive illustratethe. approximate location and position of the jet openings or holes.

The coils are supplied with precooling fluid by means of copper pipelines 38. Each of these pipe lines serves one coil and extends from suchcoil out through the roof of the inner shell and thence down through theinsulation between the inner and outer shells to a common header 39which is tapped off pipe l9; pipe I9 is the pipe by 'means of whichliquefied gas is delivered to and withdrawn from the container.

Each pipe line 38, or that portion thereof within the boot, is equippedwith a brass globe valve 40 and a low temperature pressure gauge 4| sothat the volume or amount of precooling fluid delivered by each coil atany given time can be individually controlled. This arrangement is suchthat control of the coils is flexible and such that certain coils can becut in or out in order to meet a situation wherein one portion of theinner shell structure cools more rapidly than other portions. In thisway, it is possible to cut out any certain coil or coils to obtain thedesired rate of cooling without undue or harmful temperaturedifferences.

Pipe l9 runs from the liquefaction plant 29 through the boot andterminates within the inner shell near its bottom. A valve 42 betweenpipe l 9 and header 30 enables liquid derivedfrom the liquefactionplant, to be diverted from pipe I! to header 30.

Vent 23, which extends through the boot. also connects with theliquefaction plant and serves to collect vapor or gas from the upperportion of the tank inner shell and conduct the same back to theliquefaction plant where it is either liquefled or discharged into thegas mains as gas.

The liquefaction plant receives raw natural gas through pipe 43 whichextends from gas main M to the liquefaction plant. Vent gas and gasderived from the regasification of liquid derived from the container maybe put into the gas mains through a pipe 45. a

A number of thermocouples 48 which extend through openings in the outershell, through the insulation l1 and contact the inner shell, are usedto indicate or measure the temperature at various representative partsof the inner shell structure not only during the precooling period, butalso during operation of the tank in service.

This cylindrical tank is designed to operate in conjunction with threespherical type storage tanks already in service storing liquefiednatural gas for augmenting the city gas supply.

This natural gas has the following approximate analysis by volume:

The liquid having the highest boiling point that can be obtained fromthis natural gas by proper adjustments of the liquefaction pressures andtemperatures in the liquefaction plant is one having a boiling point at2 pounds tank pressure of approximately -70 F. It was necessary,therefore, to slowly cool down this tank to about -30 F. before usingthis highest boiling point liquid in the precooling procedure. Sincenatural gas is continually vented from the three spherical tanks, it wasdecided to divide the precooling procedure into two stages, a first orgas stage and a second or liquid stage.

In order to obtain gas having the desired temperature for the firstprecooling stage, various amounts of the gas vented from the sphericaltanks were mixed with city line gas. This gas mixture was firstintroduced at about 40 F. and at a rate of 25,000 cubic feet per hour.The temperature of the precooling gas was periodically lowered about 3F. at a time by decreasing the amount of city line gas making up theprecooling mixture, until the precooling gas eventually entered theprecooling coils at about --70 F., the

temperature of the highest boiling point liquid obtainable from theliquefaction plant.

Precooling gas was conveyed to the coils and forced in the form of jetsthrough the small holes 31. These jets contacted substantially all partsof the interior of the inner shell structure.

The gas after absorbing heat from the inner shell structure wasdischarged back to the liquefaction plant through vent pipe 23.

The liquid used at the beginning of the second or liquid stage ofprecooling was a mixture consisting mainly of natural gasolines with anappreciable butane content and with very little of the other fractions.Only a very small amount of this liquid was produced but this wasdelivered to the coils and sprayed under pressure from the minute holes31 in the coils to all parts of the interior surfaces of the inner shellstructure.

It was found that when liquid instead of gas formed the precooling jets,the temperatures at the various parts of the inner shell structurebecame more nearly uniform, although temperature differences of as muchas from 30-40 F. between different parts of the inner shell structuredid exist. These temperature differences were probably caused byvariations in the heat inflow in those portions of the inner shellstructure containing the heavier metal sections and from those portionswhere the insulation thicknesses were greater and therefore the amountof stored heat larger.

The valves controlling the delivery of precooling liquid to the coilswere regulated so that a temperature difference of no more than 50 F.existed at any given time between different parts of the inner shellstructure. A temperature difference of 50 F. represents a stress of butapproximately 10,000 pounds per square inch in the metal of the innershell structure, so that such a temperature difference was consideredsafe. If one portion of the inner shell structure became too cold, thecoil supplying cooling fluid to that portion was either adjusted or shutoff until other portions of the inner shell structure were cooled to thetemperature of such part.

After a stabilized condition was reached with the warmestliquid (theliquid having the highest boiling point) that could be produced in theliquefaction plant, adjustments in such plant were made so as to producea liquid, the tem perature (or boiling point) of which was not more thanabout 50 below the highest temperature of any portion of the inner tankshell structure. This liquid was then delivered to the coils andsprayed, by means of holes 31, onto all interior parts of the innershell structure until another stabilized condition wasreached.

This procedure was carried on or repeated I until the liquid beingintroduced into the coils included all the fractions in this natural gasand of lower boiling point which was being introduced into the coils.This was so because the new liquid which accumulated in the inner shellran into and thus became part of the pool of liquid in the bottom of theinner tank shell and caused the newly introduced liquid of lowertempera: ture to boil by the heat in the liquid forming the pool. Thiscaused the liquid of the pool to become colder. 'In this way, the bottomof the inner shell was maintained at a very uniform temperaturethroughout.

After the precooling liquid had been reduced to its lowest temperature,it was also sprayed, by means of holes 31, onto all interior surfaces ofthe inner shell structure until a condition of equilibrium' wasapproached where the heat coming in through the outer shell and theinsulation, was just being absorbed by the boiling liquid Within theinner shell.

When this condition was reached, liquefied natural gas was admitted tothetank through the liquid inlet pipe l9 as rapidly as it could beproduced, until the tank was filled.

-If the vent gas from the three spherical type tanks had not beenavailable, refrigerated gas I from the liquefaction plant could havebeen used storage tank, heat continually flows from the atmospherethrough the outer shell, through the insulation and into the innershell. This heat causes evaporation'of enough stored liquefied.

natural gas to maintain the normal storage temperature of about 258 F.The vent or evaporated gas is either recycled for liquefaction or ispassed into the distribution lines after being elevated to thetemperature of the gas in such lines. This is done by passing the gasthrough a heat exchanger countercurrent to steam. Although this tank hasbeen in operation for some months, heat contained in the insulationcontinues to be removed very slowly and it will take about one yearuntil a more or less constant temperature gradient is establishedbetween the inner and outer shells of the tank.

The precooling apparatus and the thermocouples form a permanent part ofthis cylindrical storage container so that precooling operations can becarried on at a future date, if necessary. The thermocouples are alsouseful, since they will indicate settling or other failures in theinsulation.

In accordance with the provisions of the patent statutes, I haveexplained the principle and operation of my invention and thereillustrated and described a typical commercial embodiment of the same. Idesire, however, to have it understood that, within the scope of theappended claims, the invention may be practiced otherwise than hereinillustrated and described.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. In a method of precooling the inner metal shell of an insulated tankin order to condition the same to receive liquefied gas for storage, thesteps which comprise conveyin precooling fluid to the interior of suchshell, directing jets of such precooling fluid into contact withsubstantially all interior parts of such shell structure, andperiodically lowering the boiling point of the precooling fluid soconveyed, until the temperature of such inner shell structureapproximates the desired storage temperature.

2. In a method of precooling the inner metal shell of an insulated tankin order to condition the same to receive liquefied gas for storage, the

steps which comprise conveying precooling liquid shell of an insulatedtank in order to condition the same to receive liquefied natural gas forstorage, the steps which comprise conveying precooling liquid to theinterior of such shell, directing jets of such liquid into contact withsubstantially all interior parts thereof, periodically lowering theboiling point of such precooling liquid until the temperature of suchinner shell structure closely approximates the desired storagetemperature, and in maintaining a. relatively low pressure within suchshell by continuously removing gas from such shell.

4. In a method of precooling the inner metal shell of an insulated tankin order to condition the same to receive liquefied natural gas forstorage, the steps which comprise-directing into contact withsubstantially all interior parts of such shell, jets of gaseousprecooling fluid having a temperature so near the prevailing ambienttemperature that such jets will not cause harmful thermal shock orstress, gradually lowering the temperature of the gaseous precoolingfluid until such inner shell structure closely approximates boilingpoint precooling liquid available, directing into contact with all suchinterior parts of such shell, jets of pre-cooling liquid, andperiodically lowering the boiling point of the precooling liquid untilits boiling point closely approximates the desired storage temperature.

5. In a method of precooling the inner ferrous metal shell of aninsulated tank structure in order to condition the same to receive,without harmful thermal shock or stress, liquefied natural gas forstorage, the steps which comprise directing jets of gaseous fluid intocontact with substantially all interior parts of such shell,periodically lowering the temperature of such gaseous fluid until thetemperature of such inner shell is within about 50 Fahrenheit degrees ofthe temperature of the highest boiling point liquid available forprecooling, spraying substantially all interior parts of such innershell with available precooling liquid having the highest boiling point,and periodically lowering the boiling point of such liquid until thetemperature of such inner shell approxi mates the desired storagetemperature.

6. In a method of precooling the inner metal shell structure of aninsulated tank in order to condition the same to receive liquefied gasfor storage, the steps which comprise directing into contact withsubstantially all interior parts of such shell, jets of liquid having aboiling point below but so near the temperature of such interior partsas not to cause harmful thermal shock or stress thereto, andperiodically lowering the boiling point of the precooling liquidsupplied to such jets until such boiling point closely approximates thedesired storage temperature.

7. In a method of precooling the inner metal shell of an insulated tankin order to condition the same to receive liquefied gas for storage, thesteps which include directing into contact with substantially allinterior parts of such shell, jets of liquid having a boiling pointbelow but so near the temperature of such interior parts as not to causeharmful thermal shock or stress thereto and continuing with the liquidof such boiling point until a stabilized condition is reached, producinga liquid having a lower boiling point than such last liquid anddischarging jets of such liquid against all such interior parts untilanother stabilized condition is reached and in repeating such procedureuntil the temperature of such inner shell approximates the desiredstorage temperature.

9 10 8. A rnethod es set forth in cleim 6, in which the v UNITED STPATENTS precoolmg 11qu1d 1s produced 111 the same plant that liquefiesthe gas to be stored. N mb r Name Date 9. A method as set forth in claim6, in which 1,569, p a 12, 1926 the precooling liquid is produced fromthe gas to 1,638,835 Davis Aug. 16, 1927 be stored in the plant thatliquefies such gas. 1,655,954 Harold Jan. 10, 1928 JAMES O. JACKSON.2,108,017 Lithgow Feb. 8, 1938 1 2,240,364 Kimball et al. Apr. 29, 1941REFERENCES CITED 2,365,138 Morgan Dec. 12, 1944 The following referencesare of record in the file of this patent:

